The present invention relates to a satellite facility having communication function and more particularly to such satellite facility and a satellite communication system using a plurality of artificial satellites.
The satellite communication is the communication system primarily characterized by its global broadcasting function enabling a large amount of information to be simultaneously transmitted to many users. Both the cable communication and the wireless communication of ground-based station have not such function. However, development of the satellite exceptionally requires vast sums of cost as well as time and, in addition, it is difficult to equip the satellite with leading-edge technologies.
In spite of these problems, many recent commercial satellites are designed to have a lifetime in the order of 10–20 years in order to avoid an economical risk due to possible failure of launching and to reduce the cost. Even assumed that the leading-edge technologies (for example, devices, systems and protocols) can be loaded on the satellite before this satellite has been launched, it is impossible for these leading-edge technologies to follow progresses and changes of the communication technologies on the ground immediately from the launching moment. Consequently, there is an anxiety that these leading-edge technologies might become things of past.
While some experimental satellites have been launched with some efficient communication systems and achieved successful orbital travels, substantially most of the commercial satellites have conventionally been equipped only with a transponder adapted to make simple frequency conversion referred to as bent pipe relay and left mounting of regenerative transponder, base band switching equipment or the like over, although it is known that these equipments are required for efficient switching. This is for the reason that the technology or the functional lifetime often misfit the lifetime of the satellite limited by its design.
As the related art, for example, Japanese Laid-Open Patent Application Gazette No. 2001-285169 discloses a supplemental satellite communication processing system. Here is disclosed a facility basically comprises a first satellite provided with a processor and a second satellite provided also with a processor so that the second satellite is launched after the first satellite and signal processing by the processor of the first satellite is supplementally processed by the processor of the second satellite and thereby the processing capabilities of the satellite communication system are enhanced.
However, the proposal disclosed in the above-cited Gazette is nothing but a technology to complement the system with a supplemental processor in order to enhance the processing capabilities of the system and it is impossible for this technology to overcome the lifetime misfit involved by each of the satellites. In addition, this proposal is based on the premise that the first satellite is provided with main communication functions, so it is apprehended that the equipment of the first satellite might be complicated and not only the cost might increase but also the lifetime might shorten. In view of the problem as has been described above, there is a serious demand for realization of an improved satellite communication system taking account of function sharing by the respective satellite in the relationship with the lifetime of the system limited by the design and convenience for deployment.